Device for finishing complementary parts and testing the same

ABSTRACT

A device for finishing and testing complementary die or mold parts and similar complementary parts has a support plate for supporting a part to be finished in a downwardly facing position. This support plate is slidable between a lowered position in which this part and a second upwardly facing part complement or otherwise coact with each other and a raised position in which the two parts face each other spaced apart, and is also swingable into a position in which the parts are in substantially planar alignment both facing upwardly, whereby both parts are conveniently accessible for finishing. The device also includes a testing assembly for testing the complementary parts as to accuracy of fit and trueness of shape.

United States Patent [1 1 Reis et a1.

[73] Assignee: said Reis, by said Pfenning and B011 [22] Filed: Jan. 3, 1972 [21] 1 App]. No.2 214,797

Related US. Application Data [63] Continuation-impart of Ser. No. 887,500, Dec. 23,

1969, Pat. NO. 3,640,411.

[52] US. Cl. 73/37, 73/46, 249/105,

425/49 [51] Int. Cl. G01In 3/02 [58] Field of Search 73/37, 37.5, 46,

73/104; 214/315, 31.3;100/D1G. 18; 18/16 R; 425/423, 49; 249/53, 105

[56] References Cited UNITED STATES PATENTS 2,707,390 5/1955 Beretish 73/46 2,424,235 7/1947 Hofl'er 249/53 3,241,193

3/1966 Pohlman 425/D1G. 47

[ Dec. 18, 1973 Primary Examiner-Richard C. Queisser Assistant Examiner-Daniel M. Yasich Attorney-Frederick E. l-Iane et a1.

[57] ABSTRACT A device for finishing and testing complementary die or mold parts and similar complementary parts has a support plate for supporting a part to be finished in a downwardly facing position. This support plate is slidable between a lowered position in which this part and a second upwardly facing part complement or other wise coact with each other and a raised position in which the two parts face each other spaced apart, and is also swingable into a position in which the parts are in substantially planar alignment both facing upwardly, whereby both parts are conveniently accessible for finishing. The device also includes a testing assembly for testing the complementary parts as to accuracy of tit and trueness of shape.

17 Claims, 8 Drawing Figures 1 DEVICE FOR FINISHING COMPLEMENTARY PARTS AND TESTING THE SAME This application is a continuation-in-part application based on our copending application Ser. No. 887,500 filed Dec. 23, 1969 and issued as US. Pat. No. 3,650,4ll on Mar. 21, 1972.

The invention relatesto a device for finishing and testing die or mold parts and other complementary parts, and more particularly, to a device of this kind in which one part to be finished such as the top part is supported by a support member which is linearly movable toward and away from a second support member supporting thereonthe second part to be finished such as the bottom part, the first support member being also swingable from an operating position into a position for finishing the part supported on said member.

The terms finishingand testingas herein used, are intended to refer to detecting and correcting irregularities or flaws as may interfere with the operation and use of the complementary parts.

BACKGROUND Devices of the general kind above referred to as now known are generally so arranged that the first support member is suspended at an angle of about 90 relative to the second support member when the first support member is fully swung out as much as possible. The part supported by the first support member is then hanging just outside of the device, and as a result at least some portions of this part are not or at least not conveniently accessible for finishing. Convenient accessibility of the swung out suspended part is particularly important when the device such as a press is designed for finishing large parts. In such case, the operator may have to step upon an elevated platform as otherwise he would not be able to reach all portions of the part. The aforedescribed limited positioning of the part supported by the first support member which leaves this part hanging alongside the device is not satisfactory as the operator must not only mount an elevated platform, but must work overhead as the part is likely to be located at least partly above the level of his head.

Moreover, with finishing devices of the described kind it is not conveniently possible to test whether the two complementary parts accurately fit together and are accurately shaped.

THE INVENTION It is a broad object of the invention to provide a novel and improved finishing device or press of the general kind above referred to which allows convenient accessibility not only of the lower part to be finished, that is, the part supported by the second or lower support member, but also of the upper part supported by the first or upper support member, even if the overall dithe tightness of the fit between the two parts and the trueness of a mold cavity defined by the two parts.

SUMMARY OF THE INVENTION The aforepointed out objects, features and advantages, and other objects features and advantages which will be pointed out hereinafter and are set forth in the appended claims, are obtained by mounting the upper one of two parts to be finished on a support plate which can be swung out from a working position in which the two parts are in vertical alignment with each other into a position in which the two parts are at substantially the same level so that the upper part can be worked on and finished as conveniently as the lower part. The device further provides for lowering of the upper part into complementary or coacting position with the lower part for checking whether the two parts are fully satisfactory, or whether further finishing work is necessary. To effect such movement of the upper part into the position for convenient finishing, a support plate mounting this part can be swung out of the device or press by an angle of more than In many cases, a pivotal movement through about is sufficient, but it is sometimes preferable to provide for a pivotal movement through to bring the two parts into planar alignment. Guide and support means for guiding the swingable support plate while being pivoted out the device or press are preferably provided.

According to the invention, the device includes a testing assembly for injecting a testing medium, which is liquid at elevated temperature, between the two parts to check whether the same fit tightly together and have the desired inside configuration.

DETAILED DESCRIPTION OF THE INVENTION In the accompanying drawing, several preferred embodiments of the invention are shown by way of illustration and not by way of limitation.

In the drawing:

FIG. 1 is a diagrammatic elevational view of a finishing device showing the two parts to be finished in positions for movement into coaction with each other;

FIG. 1a is an elevational sectional detail view of the testing assembly of the device;

FIG, 2 is a similar elevational view of the device showing the lower part to be finished in a laterally displaced position and the support plate for the upper part swung out of the device by an angle of more than 90;

FIG. 3 is an elevational view similar to FIG. 2, but showing the support plate and the upper part thereon moved out of the device by an additional angle;

FIG. 4 is an elevational view similar to FIG. 3, but showing the support plate and the upper part thereon in a position swung out by an angle of 180, so that the two parts are substantially coplanar disposed, both facing upwardly;

FIG. 5 is an elevational diagrammatic view of a device with a modified drive means for pivoting and guiding the support plate supporting the upper part to be finished; I

FIG. 6 is an elevational diagrammatic view of a finishing device in which the guide and drive means for the pivotal support plate are further modified; and

FIG. 7 is a diagrammatic elevational view of a modification of the means for supporting the pivotal support plate for the upper part to be finished.

Referring now to the figures in detail, the exemplified finishing device as shown in FIGS. 1 to 4 comprises a cross-bar or head 1 fixedly mounted on guide members such as uprights or columns la. The columns support displaceably thereon a slidable member or ram 2, the bottom side of which has hinged thereto by means of a hinge 4 a support plate 3. Member 2 and plate 3 are up and down movable from the uppermost position of FIG. 1 into the lowermost position of FIG. 4.

The device is shown vertically arranged. Such arrangement is often the preferred one, but it should be understood that it is also within the concept of the invention to arrange members la in horizontal position in which case member 2 and plate 3 are horizontally displaceable.

Pivotal plate 3 is held in the horizontal position of FIG. 1 by a drive means 5 which when operated effects the pivotal movements of the plate into the positions shown in FIGS. 2 to 4, and more fully described hereinafter.

The base part of the device comprises a carriage or sled 6 which can be laterally displaced on a base member 7 such as a table from the position of FIG. 1 into the position of FIG. 2.

Carriage 6 supports a part 8 to be finished. This part may be visualized as the lower half of a die or mold facing upwardly. A complementary upper part 9 of the die or mold is suitably mounted facing downwardly on support plate 3. Part 9 includes ducts 116 and cavities 117 for a purpose which will be more fully explained hereinafter.

Slidable member 2 and plate 3 can be lowered into a position in which the parts 8 and 9 engage with each other. A check is then desirable whether the two parts have the required complementary shape for instance, two mold parts should engage with each other without gaps or openings therebetween and/or define a mold cavity therebetween. Such checking is effected according to the invention by injecting between the parts a suitable medium. A testing assembly suitable for the purpose such as a pressurized spray device 30 is diagrammatically indicated in FIG. 1 and is shown in detail in FIG. la.

The exemplified testing assembly comprises a container 100 secured by suitable fastening means such as screw bolts on slidable member 2. Container 100 serves as supply container for testing medium 102. The testing medium is a substance that hardens at temperatures such as room temperature but is liquid at a temperature of 120C and above. Many media are suitable for use as testing medium. The basic requirement is that the medium has a high viscosity when liquid, will change from its hardened state to is liquid state at a fairly low temperature, is essentially neutral to material with which it may come into contact and can be injected at relatively low pressures. Suitable media are various readily available types of synthetic thermoplastics materials, especially thermoplastics having a paraffin base; such plastics become liquid at about 120C. A heating element such as electric heating coils 103 jacket container 100 for holding the supply 102 at the temperature at which it remains liquid.

Space 100a in container 100 is connected via a pressure pipe 104 to a source 105 of pressurized air thereby holding this space under pressure. As shown in FIG. 1a, the bottom end of the container is closed off by the respective wall portion of member 2. This wall portion includes a discharge nozzle 106 which is normally closed by a nozzle needle 107. This needle is carried by a plunger 109 slidable in a control cylinder 108. A

compression spring 110 urges the needle into its illustrated closing position. A flexible pressure pipe 111 connects the cylinder space below plunger 109 via a control valve 112 and a pressure pipe 113 to the source 105 of pressurized air.

As it is evident, operation of valve 112, either mechanically or magnetically, will admit pressurized air into cylinder 108 below the plunger thereby lifting the same against the action of spring 1 10. The liquid injection 102 due to the pressure in space 100a is now forced through discharge nozzle 106 and a flexible hose 115 which leads via a passage 114a in plate 3 to a distributor chamber 114 within upper mold part 9. This chamber distributes the medium flowing into it through ducts 116 to the cavities 117 in the downward facing side of mold part 9. Flexible hose 115 is of a length such that it can accommodate itself to various shapes of mold parts 9 and also to different distances between slidable member 2 and plate 3. Moreover, the hose is preferably jacketed by a heating element 1150 to assure that the testing medium 102 when passing through the hose remains in its liquid state.

The testing medium will gradually fill the cavities 1 17 in part 9 until its flow is stopped by equilibrium of the pressure in cavities 117 andin container space 100a. Accordingly, no metering of the feed of testing medium is necessary. Due to maintaining the testing medium at a state of high liquidity by heating it, electrically or otherwise as described, as it passes through the device, low specific pressures are necessary to eject the testing medium from container 100 when desired. Nozzle 106, hose 115, passage 114a, chamber 114, and ducts 116 constitute a conduit means for feeding liquid testing medium between mold parts 8 and 9 as will be more fully explained hereinafter.

The injection pressure should be at least 3 kg/cm and in any event not more than 15 kg/cm As stated before, the melting point of the preferred media such as the afore mentioned thermoplastics, is 120C and above. Accordingly, the medium must be maintained at a minimum temperature of 120C. In actual practice, a temperature of about has been found very suitable since at that temperature level the thermal stability of the medium and thus the liquidity thereof are assured for a prolonged period of time such as five to eight hours.

The required pressurized air may be obtained from any suitable source as indicated at 105; the pressure pipes may, of course, be connected to any available pressure system or to a special air compressor.

As is evident, injection of the medium upon placement of mold parts 9 and 8 into a superimposed and engaged condition in the manner previously described, will readily show whether the two parts fit tightly as if there are gaps between the two parts some of the injected medium will be blown out through such gaps. As such blow-out of medium is bound to occur sooner or later, it is essential that the medium can be injected at fairly low temperatures and is also harmless on contact so that working personnel which may be hit by blownout injection medium will not be injured.

It may be pointed out in this connection that a devices as hereinbefore referred to may be a heavy press or ram weighing several tons so that the forces to be controlled are very considerable. The two parts 8 and 9 may be die parts for shaping metal or other material between the two parts when the slidable member 2 is lowered in the manner of a ram against an anvil, coacting with carriage 6 and table 7 acting as anvil.

A drive for moving the slidable member 2 up and down and a drive 5 for pivoting support plate 3 may be visualized as hydraulic drives, but of course other suitable drives can also be used.

The operation of the hereinbefore described device is apparent from FIGS. 1 to 4.

As stated before, FIG. 1 shows the device in a position in which parts 8 and 9, which may be visualized as having been finished, are ready for coaction with each other.

Let it now be assumed that parts 8 and 9 are to be finished. FIG. 2 shows the hydraulic drive 5 operated for pivoting plate 3 from the position of FIG. 1 into the position of FIG. 2. Such pivoting of the plate is effected by means of a connecting rod 13 linked by a pin 14 to one end of plate 3, the other end of which is linked to slidable member 2 by hinge 4 as previously described. The drive 5 itself, or more specifically, its cylinder 5a, is guided and supported by a rest 16 on a bracket extending from cross-bar 1. As it is seen in FIG. 2, pivoting of plate 3 through an angle of more than 90 swings the plate clear out of the way of columns la.

FIG. 2 also shows that the carriage 6 is laterally displaceable into a position spaced apart from the columns. Displacement of the carriage which is supported on rollers or wheels 6a, can be effected manually or preferably by a drive means shown as a motor releasably coupled to an axle of wheels or rollers 6a, as it is diagrammaticaly indicated in FIG. 1. The carriage is preferably displaced prior to the pivoting of plate 3.

Downward movement of slidable member 2 is effected by actuating drive 10. As is evident,such downward movement of member 2 causes plate 3 to swing out still further relative to columns la. Prior to the lowering of member 2, connecting rod 13 is released from plate 3 for return into cylinder 5a to permit a free swinging movement of the plate. The now free edge of plate 3 may slide along any suitable support surface, but it is preferable to quide the edge on guide tracks 12, rollers ll facilitating the movement of the edge along the tracks. Guide 12 is shown as an extension of table 7 and preferably hinged to the table so that it can be folded back when not in use. Cylinder 5a moves along with member 2 and is guided by rest 16 while moving downwardly or upwardly.

FIG. 4 shows the lower end position of plate 3 in which the same rests on guide tracks 12 in a position substantially coplanar with carriage 6. The mold or die part 9 is now positioned facing upwardly and is freely accessible, as is mold or die part 8. FIG. 4 also shows that cylinder 5a is now in an approximately vertical position so that it does not interfere with working on mold or die part 8. I

Part 8, together with its carriage, may be lifted if necessary by suitablehoist means. There is schematically shown, by way of example, a hoist motor secured by a bracket 41 to table 7. A frame 42 serves to support hoist ropes 43 and 44 guided over suitable pulleys 45 and detachably secured to carriage 6, as it is indicated at 46.

Referring to FIG. 5, the hydraulic drive means 5 and more specifically, the cylinder 5a thereof, is hinged to about the middle of sliding member or ram 2. As this member is lowered, the cylinder is guided by an abutment surface 17 on cross-bar 1.

The figure shows the working position of the device in full lines, the movable parts being shown in an intermediate position (corresponding to FIG. 2) by dasheddotted lines, and in the end position (corresponding to FIG. 4) by dashed lines.

According to FIG. 6, cylinder 5a of hydraulic drive means 5 is guided by a rope or chain 18 attached at one end to sliding member 2 and at the other end to cylinder 5a. An intermediate point of the rope is guided over a pulley 19 on cross-bar l.

The fully raised position of member 2 and cylinder 5a is shown in full lines and the lowered position of the member and the cylinder is shown in dashed lines. As previously explained, the nearly vertical position of the cylinder when lowered, serves to provide a clear space for working on die or mold part 8. 1

T o facilitate working on the upper die or mold part 9 when plate 3 is tilted out of its substantially horizontal position (see FIG. 1) through an angle of more than (see FIG. 2),;the plate is supported and guided by guide 12 pivoted to table 7, as already mentioned. The guide can also be mounted separate from the device either on the floor or on a separate platform.

As previously described, pivoting of support plate 3 is again effected by means of hydraulic drive means 5 and the connecting rod 13 which is linked at one end to plate 3 by pin 14. The same end of the plate also mounts rolls or coasters ll.

FIG. 7 shows an arrangement in. which pin 14 is held in a claw 20 on the end of rod 13. The claw is open on its side facing support plate 3 and formed with a guide surface 21, the purpose of which will be more fully explained hereinafter. Guide 12 extending from table 7 mounts a curved guide surface 23.

The figure shows support plate 3 and claw 20 in three different operational positions designated by A, B and C.

In the pivotal position A,'pin 14 is still retained in claw 20. As connecting rod 13 is being further pushed out of the cylinder of drive 5, the lower dead point position of plate 3 and the mold or die part 9 (not shown in FIG. 7) thereon is finallyreached.

Upon continued outward movement of rod 13 beyond this dead point position, the position B is reached. In this position guide surface2l becomes engaged with pin 14 and will cause the pinto slide out of the claw when the weight of rod '13 swings the same back into the vertical position. The curved surface 23 serves to assure that pin 14 will actually leave claw 20 as will be more fully explained hereinafter.

After the position B is reached, the sliding member 2 is preferably lowered by means of its drive (drive 10) in the direction of arrow 22, so that the support plate 3 eventually reaches the position in which its roller 11 rests on curved surface 23. Further lowering of member 2 now moves plate 3 into the position C and finally into its lower horizontal position (see FIG. 4).

Pin 14 is freed of claw 20 as the rod 13 and thus the claw participate in the movement of sliding member 2 while pin 14 continues its relative movement in the direction of the pivoting of plate 3.

The control of drives 5 and 1001f the device is preferably so arranged that the aforedescribed sequence of movements of the plate while being pivoted and also reaching either end position is assured and occurs automatically in both directions.

While the testing assembly 30 is only shown in connection with the structure of FIG. 1, it can, of course, be installed on the other illustrated structures also.

The invention is not limited to the illustrated and described embodiments. The details of the structure can be modified in accordance with specific requirements without departing from the basic concept of the invention. Moreover, as stated before, the entire device may be arranged in horizontal position, that is, in a position in which the members la are horizontal while the crossbar 1, the sliding member 2 and the table 7 are vertical.

What is claimed is:

1. A device for finishing and testing complementary mold parts, die parts and other complementary parts, said device comprising in combination:

a base member for supporting a first part to be finished;

a slidable member;

guide members slidably guiding said slidable member for linearly displacing the same relative to the base member;

a support plate for supporting thereon a second part to be finished, said first and second parts being movable into a superimposed and engaged position by lowering said slidable member;

hinge means hinging the support plate to the slidable member, said support plate being pivotal between a position substantially parallel to the slidable member and an angular position more than 90 out of said parallel position;

a guide means extending from said base member substantially planar therewith, said guide means constituting a support and a guide for the support plate as the same is being pivoted relative to the slidable member; and

a testing assembly for testing the fit of said parts and the trueness of a mold cavity between said parts in the superimposed and engaged position thereof, said testing assembly comprising a supply container for a liquid testing medium, a conduit means connected to said container and to one of said first and second parts and between said parts in the superimposed and engaged position thereof, pressure means communicating with said container for increasing the pressure therein above atmospheric pressure, and control means for releasing a flow of the testing medium from the container through said conduit means. 7

2. The device accordingto claim 1 wherein the second part to be finished and tested is a part including at least one cavity on its side facing the first part in the superimposed and engaged position of the parts, and said conduit means is connected with said cavity, said control means closing the flow of the testing medium through the conduit means in response to pressure equilibrium between the container and the cavity.

3. The device according to claim 2 wherein said container is supported on said slidable member, said conduit means extending through said support plate.

4. The device according to claim l wherein said support plate is pivotal through an angle of about 180 out of said parallel position.

5. The device according to claim 1 wherein said guide means is hinged to the base member.

6. The device according to claim 1 wherein said pivotal support plate is hinged at one edge to the slidable member, and wherein roller means are mounted at an opposite edge of the support plate, said roller means engaging said guide means during pivoting of the support plate.

7. The device according to claim 1 and comprising a first drive means including a connecting rod, and hinge means linking said connecting rod to said pivotal support plate, and a second drive means drivingly coupled to said slidable member at about the middle thereof for displacing said member, said first drive means being supported by said slidable member.

8. The device according to claim 7 wherein said hinge means are releasable.

9. The device according to claim 7 wherein said pivotal support plate is hinged at one edge tp said slidable member, and said hinge means linking the rod to the support plate is mounted at an opposite edge of said plate.

10. The device according to claim 9 wherein a crossbar extends across said guide members attached thereto at a fixed distance from said base member, and guide means on said cross-bar to guide said first drive means for controlling the position of the first drive means during displacement of the slidable member by the second drive means.

11. The device according to claim 10 wherein said cross-bar includes an abutment member, said first drive means abutting against said abutment member when the pivotal support plate is in its angular limit position out of its position parallel to the slidable member.

12. The device according to claim 10 wherein said guide means comprises a rope secured at one end to said slidable member and at the other end to said first drive means, said rope being guided at an intermediate point by a guide means on said cross-bar.

13. The device according to claim 1 wherein said guide members are uprights guiding said slidable member for lowering the same to a level just above the top level of the base member.

14. The device according to claim 1 wherein a carriage for supporting thereon said first part to be finished is displaceable on the base member for moving said carriage and the part thereon into a position laterally spaced from the guide members.

15. The device according to claim 14 wherein a drive means is coupled to the carriage for laterally displacing the same.

16. The device according to claim 14 and comprising hoist means for lifting the carriage in the laterally displaced position thereof.

17. The device according to claim 1 wherein a drive means is releasably coupled to the support plate by coupling means for pivoting the support plate, said coupling means including an open claw supported by the dirve means and a pin on the plate, said pin sliding out of the claw in a predetermined pivotal position of the support plate but remaining engaged therewith in all other pivotal positions of the plate. 

1. A device for finishing and testing complementary mold parts, die parts and other complementary parts, said device comprising in combination: a base member for supporting a first part to be finished; a slidable member; guide members slidably guiding said slidable member for linearly displacing the same relative to the base member; a support plate for supporting thereon a second part to be finished, said first and second parts being movable into a superimposed and engaged position by lowering said slidable member; hinge means hinging the support plate to the slidable member, said support plate being pivotal between a position substantially parallel to the slidable member and an angular position more than 90* out of said parallel position; a guide means extending from said base member substantially planar therewith, said guide means constituting a support and a guide for the support plate as the same is being pivoted relative to the slidable member; and a testing assembly for testing the fit of said parts and the trueness of a mold cavity between said parts in the superimposed and engaged position thereof, said testing assembly comprising a supply container for a liquid testing medium, a conduit means connected to said container anD to one of said first and second parts and between said parts in the superimposed and engaged position thereof, pressure means communicating with said container for increasing the pressure therein above atmospheric pressure, and control means for releasing a flow of the testing medium from the container through said conduit means.
 2. The device according to claim 1 wherein the second part to be finished and tested is a part including at least one cavity on its side facing the first part in the superimposed and engaged position of the parts, and said conduit means is connected with said cavity, said control means closing the flow of the testing medium through the conduit means in response to pressure equilibrium between the container and the cavity.
 3. The device according to claim 2 wherein said container is supported on said slidable member, said conduit means extending through said support plate.
 4. The device according to claim l wherein said support plate is pivotal through an angle of about 180* out of said parallel position.
 5. The device according to claim 1 wherein said guide means is hinged to the base member.
 6. The device according to claim 1 wherein said pivotal support plate is hinged at one edge to the slidable member, and wherein roller means are mounted at an opposite edge of the support plate, said roller means engaging said guide means during pivoting of the support plate.
 7. The device according to claim 1 and comprising a first drive means including a connecting rod, and hinge means linking said connecting rod to said pivotal support plate, and a second drive means drivingly coupled to said slidable member at about the middle thereof for displacing said member, said first drive means being supported by said slidable member.
 8. The device according to claim 7 wherein said hinge means are releasable.
 9. The device according to claim 7 wherein said pivotal support plate is hinged at one edge tp said slidable member, and said hinge means linking the rod to the support plate is mounted at an opposite edge of said plate.
 10. The device according to claim 9 wherein a cross-bar extends across said guide members attached thereto at a fixed distance from said base member, and guide means on said cross-bar to guide said first drive means for controlling the position of the first drive means during displacement of the slidable member by the second drive means.
 11. The device according to claim 10 wherein said cross-bar includes an abutment member, said first drive means abutting against said abutment member when the pivotal support plate is in its angular limit position out of its position parallel to the slidable member.
 12. The device according to claim 10 wherein said guide means comprises a rope secured at one end to said slidable member and at the other end to said first drive means, said rope being guided at an intermediate point by a guide means on said cross-bar.
 13. The device according to claim 1 wherein said guide members are uprights guiding said slidable member for lowering the same to a level just above the top level of the base member.
 14. The device according to claim 1 wherein a carriage for supporting thereon said first part to be finished is displaceable on the base member for moving said carriage and the part thereon into a position laterally spaced from the guide members.
 15. The device according to claim 14 wherein a drive means is coupled to the carriage for laterally displacing the same.
 16. The device according to claim 14 and comprising hoist means for lifting the carriage in the laterally displaced position thereof.
 17. The device according to claim 1 wherein a drive means is releasably coupled to the support plate by coupling means for pivoting the support plate, said coupling means including an open claw supported by the dirve means and a pin on the plate, said pin sliding out of the claw in a predetermined pivotal position of the support plate but remaining engaged therewIth in all other pivotal positions of the plate. 